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The Effect of Inhibitors on the Rate of Sucrose Crystallization in Whey Protein Films
By,
K. L. DANGARAN and J.M. Krochta
Department of Food Science and Technology
University of California, Davis
Whey protein isolate (WPI) films plasticized with sucrose are high in
gloss and have excellent oxygen barrier properties. As coatings, whey
protein/sucrose solutions may be used as water-based replacements for
alcohol-based shellac coatings. In prior studies it was determined that
as sucrose content of WPI films and coatings was increased, the
appearance, barrier and mechanical properties were improved. However,
over time gloss of coatings faded and films became weak and brittle.
This was attributed to sucrose in the films and coatings changing from
amorphous to crystalline state. In a past study, it was determined that
cross-linked, denatured WPI films decreased the rate constant for
sucrose crystallization significantly more than native films.
The objective of this study was to determine the effect of
crystallization inhibitors on sucrose crystallization rate constants in
denatured WPI films. The four inhibitors studied were lactose, raffinose,
modified starch and polyvinylpyrrolidone. A WPI/sucrose film without
inhibitor was included as control.
Films were made and then stored at constant temperature in four
different relative humidities (23%, 33%, 44% and 53%). The weight of
each film was measured periodically to monitor crystallization. When
amorphous sucrose crystallizes, it loses water, and the weight of the
film decreases. By modeling the data with the Avrami equation for
crystallization kinetics, the rate order and rate constants for sucrose
crystallization in WPI/sucrose films could be determined.
Studies monitoring the WPI films at the four relative humidities showed
that lactose, raffinose, and polyvinylpyrrolidone decreased the rate
constant of sucrose crystallization compared to the control. The effect
became more significant as the relative humidity increased.
Results from this study will be used to develop high gloss, water-based
WPI coatings that do not experience deleterious sucrose crystallization.
This will prevent loss of gloss and durability of the coatings over
time.
For more information on Dr. Krochta’s work and the Food Science and Technology Department at UC Davis, please visit Dr. Krochta's Web site - http://foodscience.ucdavis.edu/fst/faculty/KrochtaWeb/index.htm.